forces (p5) Flashcards
what is a scalar quantity, and give an example:
- scalar quantities only have a magnitude (size). they do not have a direction.
- mass, temperature, speed, distance, time, energy.
what is a vector quantity, and give an example:
- vector quantities have both a magnitude (size) and a direction.
- displacement, weight, force, velocity, acceleration, momentum.
define ‘mass’:
- a measure of the amount of matter in an object.
- not determined by gravity.
- stays the same wherever you are in the solar system.
- is not a force.
define ‘weight’:
- a measure of the force of gravity acting on an object.
- determined by gravity.
- changes depending on where you are in the solar system.
- is a force.
define energy transfer and work done:
- whenever a force is used to move an object, energy is transferred. scientists call this work.
- work is simply a measure of energy transfer, so the unit of work is the joule. when a force of 1N moves an object by 1M, 1J of work has been done.
define ‘centre of mass’:
the weight of an object may be considered to act at a singular point.
- however, the centre of mass of an object may not necessarily be in its centre; this would only occur if the object is uniform in shape and density.
when you balance an object on one point, what determines when it topples over?
let’s say a square is balancing on one corner. as it’s uniform in shape and density, the centre of mass is in its centre.
- if you were to push the object, but its centre of mass doesn’t surpass the point of contact, it falls back.
- if you were to push the object, and its centre of mass surpasses the point of contact, it falls forward, as it is unbalanced.
define ‘elastic deformation’:
when objects deform elastically, they still hold the ability to return to their original shape.
- Hooke’s law only works when an object behaves elastically.
define ‘plastic deformation’:
when objects deform plastically, they can no longer return to their original shape.
what are the three variables for the Hooke’s law required practical?
- independent (x axis):
force applied - dependent (y axis):
extension of spring - control:
room temperature, diameter of spring, starting length of spring, spring material
describe the method for the Hooke’s law required practical:
- measure original length of the spring using a ruler.
- set up the equipment as shown in the diagram (you should be able to picture the set-up).
- attach a known weight (1N) to the spring. wait for the spring to stop moving.
- measure the new length of the spring.
- calculate the extension of the spring by subtracting the original length from the new length of the spring.
- repeat steps 2-4 with weights up to 5N.
- plot a scatter graph with the force on the x axis and the extension on the y-axis. the graph should show a directly-proportional relationship.
what is the biggest source of uncertainty in the Hooke’s law required practical?
- the biggest source of uncertainty is in the measurement of the spring, using the human eye. a parallax error (random error) could occur, so you must get to eye-level to obtain the most accurate reading.
what has occurred if the line of best fit on a Hooke’s law graph stops being straight?
this shows that the spring has reached its elastic limit. it has become plastically deformed, and has therefore skewed the results of the practical, as Hooke’s law only works when the object is elastically deformable.
what is Hooke’s law?
force is directly proportional to extension.
- as an equation, this is F = ke, where k is a constant.
- force (N), spring constant (N/m), extension (m).
describe the pressure in a column of fluid:
- take a column of water. the water at the bottom of the column would be under a much higher pressure than the water at the top. the mass of the particles pushing down on the water at the bottom of the container creates more pressure.
- the deeper the liquid, the greater the pressure.
